Method of making thread dies



Aug. 20, 1929. J. BATH 1,725,246

METHOD OF MAKING THREAD DIES Filed July 19, 1924 5 Sheets-Sheet l &

' J0 J2: emzar' T2 D 70% 345% Aug. 20, 1929. J. BATH 1,725,246

' IETHOD OF MAKING THREAD DIES Fil d y 19, 1924 3 Sheets-sheet 2 Aug. 20, 1929. J B 1,725,246

METHOD OF MAKING THREAD DIES Filed ly 19, 1924 3 Sneexs-Sheet 3 Patented Aug. 20, 1929.

UNITED STATES JOHN BATH, OF WORCESTER, MASSACHUSETTS.

METHOD OF MAKING THREAD DIES.

Application filed July 19,

This invention relates to an improved method of making thread dies and other similar articles by which method the accuracy of the dies is much increased and the durability of the dies is prolonged.

It has been customary, in the manufacture of thread dies and other similar articles, to cut aseries of parallel grooves lengthwise of the die in any convenient manner, as by one or more V-shaped milling cutters. The grooved die is then hardened which operation seriously affects the accuracy of the die, as the threads of the die after hardening will not be in exact alignment.

It is the object of my invention to greatly improve upon this old method of making thread dies. In accomplishing this result, I first subject the die blank to the required heat treatment to harden the die, and thereafter cut the threads in the face of the hardened die by a grinding wheel which is given repeated relative movement across the face of the die, thus grinding the threads from the solid hardened blank. N 0 further heat treatment is necessary and the die retains its perfect accuracy.

In the drawings I have shown parts of a grinding machine on which my improved method may be conveniently carried out.

Fig. 1 is a partial plan view of a grinding machine by the use of which my improved method may be practiced;

Fig. 2 is a partial side elevation of the machine shown in Fig. 1

7 I Fig. 3 1s a sectional front elevation, taken along the line 33 in Fig. 2;

Fig. 4 is a detail sectional side elevation, taken along the line 44 in Fig. 3;

Fig. 5 is a front elevation of the wheel shaft bearing or slide, and the adjusting mechanism therefor;

Fig. 6 is a detail plan view of a die block, and the means for positioning the same;

Fig. 7 is a perspective view of a gauge bar for use in positioning the die block;

Fig. 8 is a perspective view of one of the spacing blocks for locating the gauge bar; and

Fig. 9 illustrates a method by which the depth of the thread may be conveniently measured.

Referring to the drawings, I have shown a grinding wheel W mounted on a wheel shaft or spindle 20 (Fig. 5) which is rotatable in bearings 21 on a Wheel slide 22 Which 1924. Serial No. 727,081.

is vertically movable in guide-ways 23 on a post or column 24 forming a part of the machine frame. An adjusting screw 25 is rotatable in a fixed bearing 26 at the top of the column 24 and is threaded in a nut fixed to the slide 22. A hand wheel 27 is secured to the upper end of the adjusting screw 25 and a graduated index plate 28 co-operatcs with an index finger 29 to show the amount of angular adjustment. The Wheel W may be driven in any convenient manner as by a sprocket 30 (Fig. 5) and chain 31 (Fig. 1) from a motor 32.

The thread die D is supported in any convenient manner upon a work support 33 (Figs. 1 and 3) which is slidable axially beneath the grinding wheel in guide-ways 34 (Fig. 4) in a table 35. The table 35 is supported in guide-ways 36 formed in an upper surface of the machine bed 37 for movement transverse to the axis of the wheel shaft.

The work support 33 is adjusted on the table 35 by means of an adjusting screw 40 (Fig. 3) having a bearing in a plate 41 fixed to the end of the work support 33. The screw 40 is threaded into a nut 42 fixed on the table 35. A gear 43 is fixed to the end of the adjusting screw 40 and is engaged by an intermediate gear 44. A secondintermediate gear 45 rotates with the gear 44 and is engaged by an adjusting pinion 46. 1

The pinion 46 is mounted to be rotated by an arm 47 pivoted at 48 on a stand 49. The arm 47 is provided with a handle 50 and also with a spring plunger 51 which is normally projected inward to engage a stop 52. The stop 52 is fixed in the stand 49 previously described which stand is mounted for angular adjustment on the plate 41, which is fixed to the end of the work support 33 (Fig. 3).

The intermediate change gears 44 and 45 and the adjusting pinion 46 are adjustably mounted on the arm 49 and these gears may be selectively arranged to provide any desired axial movement of the work support 33 for each single rotation of the arm 47. In the use of this machine for grinding plate dies I preferably select the gears so that one rotation of arm 47 will produce axial movement of the work support exactly equal to the pitch of the thread die.

lVhen it is desired to feed the work support, the yielding plunger 51 (F l) is withdrawn, permitting the arm 47 to swing downward past the stop 52. The plunger isthen released and the arm is rotated until the plunger again engages the stop 52.

The table 35 may be moved longitudinaliy in any convenient manner and I have indicated in Fig. 1 a rod 60 connected at one end to the table 35 and extending through a bearing 61 into a hydraulic cylinder 62 where it may be connected with a piston for longitudinal movement as is common in hydraulic table feeds.

The thread die D may be located and secured on the work support 33 in any convenient. manner but in the drawings I have shown the die as supported upon a magnetic chuck 63clampod to the work support 33 and rendered operative by a current of electricity delivered thereto through a cable 64: (Fig. 1).

As a means for accurately positioning the thread die upon the chuck 63 I have provided a gauge bar 65 (Figs. 6 and, 7) having a pair of cylindrical projections 66 and 67. An angle iron 68 (Fig. 8) is secured to the side of the chuck 63 and is provided with an edge 69 (Fig. 6) which is exactly parallel to the path of travel'of the table 35. One projection 66 on the gauge bar 65 may be caused to engage the edge 69 of the angle iron and the other projection 67 may be spaced from the edge 69' by inserting precision gauge blocks 70 of the desired thickness. The gauge bar 65 will thus be accurately located,the principal involved being that of the well known sine bar. A stop 71 may be fixed to the chuck 63 to locate the thread die lengthwise.

I have also provided wheel trimming devices 72 (Fig. 1) which are mounted on the wheel slide. 22 and are thus movable vertically and axially therewith. For a complete description of these wheel trimmings devices reference is made to my co-pending application No. 660689, filed by me September 4t, 1923.

In Fig. 9 I have indicated the thread die D as projecting slightly beyond the chuck 68 forconveni'ence in measuring the depth of the thread. For this purpose a round wire 74: of a definite diameter may be placed in a groove and the thickness from the bottom of the die D to the top of the wire 74 may be conveniently measured by a micrometer 7 5. In this way the depth of the parallel grooves in the die D may be easily compared and kept uniform and the exact depth of the out may also be determined, if desired, by making a suitable computation.

Suitable means is provided for effectively lubricating the wheel and the work during the grinding operation. For this purpose I have indicated in Fig. 3 a pair of nozzles 7 6 by which a suitable lubricant may be dewheel at its point of engagement with the work.

Having fully described a mechanism suitable for the carrying out of my improved method of producing thread dies, I will now describe the exact procedure by which the dies are produced.

The blank is first accurately finished on its various surfaces, and is then hardened. The die blank is then accurately located on the work support, as indicated in Fig. 6, so that the threads will be ground at the desired angle to the side of the die. The electric current is then turned on to energize the chuck and hold the die block firmly in position. The mechanism for reciprocating the table is placed in operation and the grinding wheel is gradually lowered, taking successive cuts until a groove of approximately the desired depth is ground into the surface of the hardened and tempered die block The wheel is then raised and the arm 47 is given one turn to move the die block axially of the wheel a distance exactly equal to the pitch of the desired thread.

The grinding operations are then repeated and this process is continued until grooves of approximately the desired depth have been cut across the width of the block, the depth of cut being tested as often as desired by the device indicated in Fig. 9. After the block has been thus provided with a series of grooves across its entire face, a finishing cut is made over the entire series of grooves, removing a few thousands of material in each groove and bringing all of the grooves to uniform depth.

During the grinding operation, the wheel is kept accurately trimmed by means of the trimming devices mounted on and movable with the wheel slide. The edge of the wheel isthus kept in the same axial plane and the trimming mechanism is so designed that the reduction in wheel diameter caused by trimming is accurately indicated, so that the wheel after trimming may be lowered by the hand wheel 27 to compensate for the material removed in grinding.

After the thread die is thus ground, it is ready for use and the accuracy of the die is not destroyed by heat treatment of any sort after the grooves are cut therein.

An index line on the table 35 and an index plate 81 adjustable on the work support 33 enable me to reset the wheel accurately with the work whenever desired.

The term die block should be understood to cover thread chasers and other articles of similar form and use.

Having thus described my invention and the advantages thereof, I do not wish to be limited to the details herein disclosed otherwise than as set forth in the claims, but what livered in large quantities to the grindingI claim is 1. The method of making a thread die from a pre-finished and pre-hardened die block which consists in grinding successive parallel grooves from the hardened die block, in causing a relative axial movement between the wheel and the die block equal to the desired pitch of the thread between the cutting of successive grooves, said grooves being of approximately equal depth, and in then removing a very thin layer of material by a finishing grinding cut over all of said grooves.

2. The process of making thread dies from a finished and hardened die blank, which consists in cutting a thread groove in the solid metal of said hardened die blank by repeated grinding operations, feeding the die axially relatively to the wheel, a space equal to the pitch of the thread between the grinding of successive thread grooves, maintaining a true wheel by treatment thereof between successive cuts and simultaneously with said setting of the die, while maintaining the wheel edge in its same plane of rotation.

In testimony whereof I have hereunto afiixed my signature.

JOHN BATH. 

